It has been prevailingly required to determine the concentration of alcohol contained in a liquid containing water and ethyl alcohol, isopropyl alcohol, or the other alcohol, e.g. an alcoholic beverage, fountain solution employable for printing methods including a lithographic printing method, an offset printing method, or the like.
The most practical method for sensing the concentration of alcohol contained in a liquid containing water and alcohol is to employ a hydrostatic balance.
In addition to a method in which a hydrostatic balance is employed, employable is a method in which the specific gravity of the liquid containing water and alcohol is determined, after it is drawn to a vessel. However, this method is involved with a drawback in which this method is identified as a non-continuous one because some quantity of the liquid containing at least alcohol must be drawn to a vessel.
To remove this drawback, an alcohol concentration sensor which is illustrated in FIG. 1 was developed. Referring to the drawing, a vessel-like member 3 having an opening on one side thereof (the bottom side in the drawing) is held over a liquid 1 containing alcohol therein, remaining a closed space exposed to the natural surface of the liquid 1. The vessel-like member 3 is provided an inlet 2 through which the air is supplied into the closed space, an outlet 2 through which the mixture of the air and the vapor of alcohol is purged. A gas sensor 6 is provided to the vessel-like member 3 for sensing the concentration of alcohol contained in the mixture of the air and the vapor of the liquid confined in the vessel-like member 3.
When the foregoing improved alcohol concentration sensor is employed, the vapor remained in the closed space of the vessel-like member 3 is once purged by flowing the air through the inlet and outlet 2. After the closed space of the vessel-like member 3 is purged, a predetermined length of time (This length of time can be determined by conducting experiments for plural liquid mixtures having a variety of alcohol concentration.) is given to allow the liquid 1 to allow alcohol to evaporate to the extent where the alcohol concentration of the mixture of the air and alcohol vapor represents the alcohol concentration of the liquid 1 containing alcohol. Thereafter, the gas sensor 6 is employed to determine the concentration of alcohol contained in the mixture of the air and alcohol vapor confined in the closed space of the vessel-like member 3. Based on the results determined by employing the gas sensor 6, the concentration of alcohol contained in the liquid 1 containing alcohol is determined.
Therefore, a continuous measurement is impossible, even with the foregoing improved alcohol concentration sensor.
Incidentally, since the saturation vapor pressure of alcohol varies depending on the temperature of the vapor, the rate at which alcohol evaporates from the liquid 1 depends on the temperature of the vapor or of the liquid. This means that the concentration of alcohol determined to be contained in the mixture of alcohol vapor and the air, cannot precisely represent the concentration of alcohol contained in the liquid containing alcohol, even if such determination is conducted at a time when the aforementioned predetermined time has passed after the commencement of supply of the air into the closed space of the vessel-like member 3.
Therefore, for the purpose to remove the foregoing two independent drawbacks including (a) the batch type sensing is inevitable and (b) an error caused by variation of temperature of the vapor is inevitable, an alcohol concentration sensor which is capable of continuous measurement and which is provided with a means for correcting the error caused by the temperature of the mixture of the air and alcohol, was developed.
Referring to FIG. 2, a porous polymer tube 7 which exclusively allows volatile materials to pass, alcohol in this case, and prevents the other materials, water in this case, from passing through, and of which one end is connected with an air inlet tube 5 provided with an air supply pump 4 and of which the other end is connected with an outlet tube 5 provided with a gas sensor 6 therein. In addition, a thermometer 8 is provided, in the neighborhood of the above porous polymer tube 7.
When this more improved alcohol concentration sensor is employed, the porous polymer tube 7 is soaked in a liquid 1 containing alcohol, and the air is allowed to flow through the connected tube which is a connection of the inlet tube 5, the porous polymer tube 7 and the outlet tube 5, to allow alcohol contained in the liquid 1 containing alcohol to evaporate through the porous polymer tube 7. The gas sensor 6 senses the concentration of alcohol contained in the gas mixture containing the air and alcohol flown out of the porous polymer tube 7 to the outlet tube 5. The determined alcohol concentration is corrected, following the temperature determined by the thermometer 8.
The foregoing type alcohol concentration sensor sufficiently works exclusively for the liquid containing little volume of foreign materials e.g. the finished alcoholic beverage or the already brewed liqueur. On the contrary, if a sample liquid 1 contains insoluble foreign materials, as is in the case of a liqueur under brewing, a fountain water employable for a lithographic printing method, the foreign materials e.g. sludge produced during brewing or printing, etching solution which is added into fountain water for adjusting the pH amount thereof, covers the internal surface of the porous polymer tube 7, resultantly preventing alcohol from passing therethrough. This causes a drawback in which an error increases to a remarkable extent, following the employment of the alcohol concentration sensor. In other words, the longer the alcohol concentration sensor is employed, the larger the error becomes. Results of experiments indicate that an employment of the foregoing more improved alcohol concentration sensor for 40 days causes an increase in the error by approximately 10%.
Therefore, the objects of this invention is to provide a variety of alcohol concentration sensors which is capable of accurate and continuous measurement, even in cases where a liquid contains not only water and alcohol but also insoluble foreign materials, such measurement being possible for a long period with a high grade of accuracy, regardless of a variation of the temperature of the liquid and/or the ambient atmosphere, a variation of the resistance or the pressure of the liquid flow pass, a variation of the humidity of the gas mixture, a variation of the depth of the liquid, etc.